Just wanted to stay if you implement a more sophisticated text engine to support Arabic I would purchase the Affinity Designer. You can take a look into harfbuzz, it's open source and is used as text shaping engine in firefox.
Some other features which is necessary for typography:
1. Ability to insert a glyph from a font. The glyph could have a unicode or not.
2. More languages in the character>language panel.
3. Ability to disable and enable more sophisticated typographic feature like contextual alternates.
If you need any feedback and help regarding typography features in the app I would be glad to contribute.